1. Field of the Invention
The present invention relates to a method of producing aromatic ring-containing amino compounds by hydrogenating an aromatic dinitrile compound in the presence of a solid catalyst and relates to the catalyst for use in such a production method.
2. Description of the Prior Art
A method of producing an aromatic ring-containing amino compound by a catalytic hydrogenation of an aromatic dinitrile compound in the presence of a solid catalyst to reduce the cyano group has been known. In most cases, the solvent for such a method is wholly or partly composed of liquid ammonia. As the solid catalyst, proposed are nickel and/or cobalt-containing catalysts (JP 53-20969B, UK Patent 1149251 and UK Patent 852972) and palladium-containing catalysts (JP 51-24494B, JP 2004-269510A, UK Patent 814631 and WO 2005/026101). It is taught that amine compounds are produced in a good reaction selectivity in the proposed methods because the unfavorable side reaction is prevented by the use of liquid ammonia solvents. However, the proposed methods involve serious drawbacks because the liquid ammonia solvent dissolves the catalytic metal component to destabilize the catalytic activity, a high-pressure apparatus is needed because of a high vapor pressure of liquid ammonia, and a process for vaporizing, recovering and recycling liquid ammonia is intricate to increase production costs.
As a method using no liquid ammonia, proposed is a hydrogenation using a sponge-form nickel and/or cobalt catalyst (Raney, trademark) in an organic solvent such as lower alcohols and ether compounds (JP 38-8719B and JP 54-41804A). The method of using the sponge-form catalysts involves drawbacks because the preparation of the sponge-form catalysts requires a leaching step using a chemical and a step of replacing the leaching aqueous solution with a reaction solvent, the catalyst is easily re-oxidized by oxygen, and the catalyst has a poor moldability. In the hydrogenation using the sponge-form catalyst, since a basic inorganic compound is also used to increase the reaction selectivity, an additional treatment for removing the basic inorganic compound is required after the reaction, to make the production system disadvantateous.
It is well known in the art that the catalytic hydrogenation of nitrile compounds can be performed generally under mild conditions (reaction temperature, pressure, etc.) in the presence of a noble metal catalyst rather than a catalyst containing a base metal such as nickel and cobalt because of a higher hydrogenating activity of the noble metal catalyst (Practical Catalytic Hydrogenation, Morris Freifelder (1971) John Wiley & Sons, Inc., Chapter 12 Nitriles p 240, and Studies in Surface Science and Catalysis,vol. 27, Catalytic Hydrogenation, L. Cerveny (1986) Elsevier, Chaper 4 Hygrogenation of Nitriles, p 105-144). Therefore, the hydrogenation in an organic solvent in the presence of a noble metal catalyst would provide an economically best production method, if such a hydrogenation can be effectively carried out. However, it has been known that the hydrogenation using a palladium catalyst without liquid ammonia produces, in addition to primary amines, by-products such as secondary amines and tertiary amines due to intermolecular condensation, even when a simple compound such as aliphatic mononitrile is used as the starting compound (UK Patent 962235, JP 2002-226440A, and Comparative Example B, Part I of U.S. Pat. No. 3,923,891). Therefore, it is difficult to avoid the by-production of high-boiling products in the hydrogenation of a compound having two or more cyano groups.
It has been also known that the hydrogenation of an aromatic nitrile compound using a palladium catalyst causes another side reaction in addition to the side reaction mentioned above, in which the aminomethyl group of the hydrogenated product is further subjected to hydrogenolysis to a methyl group (Comparative Example B, Part I of U.S. Pat. No. 3,923,891 and Examples 1 and 2 of U.S. Pat. No. 4,482,741). For example, it is reported that the yield of 1,3-bis(aminomethyl)benzene in the hydrogenation of isophthalonitrile in 2-methoxyethanol using a palladium catalyst is as low as 60%, showing the by-production of large amounts of high-boiling products due to intermolecular condensation and methylbenzylamine due to hydrogenolysis (Examples 1 and 2 of U.S. Pat. No. 4,482,741).
Therefore, it is absolutely necessary to prevent the above side reactions for the efficient production of the aromatic ring-containing amino compound by the hydrogenation of one or two cyano groups of an aromatic dinitrile compound to aminomethyl group using a palladium catalyst in the absence of ammonia. To prevent the side reactions, it has been proposed to add an additive to the reaction system. For example, it has been reported that a mixture of cyanobenzylamine and bis(aminomethyl)benzene is obtained in high yields by the hydrogenation in methanol solvent added with tetraalkylammonium hydroxide (JP 2002-205980A). It has been also reported that xylylenediamine is produced in high yields by introducing carbon dioxide gas into the reaction system (JP 56-63944A). However, the proposed method are disadvantageous because the decomposition of tetraalkylammonium hydroxide or the precipitation of insoluble carbonates occurs after the hydrogenation, to make the process difficult to operate, and because an additional step or apparatus for supplying or removing the additive is required.
As noted above, the method of producing an aromatic ring-containing amino compound by the hydrogenation of an aromatic dinitrile compound using a supported palladium catalyst has been reported in many known documents. However, none of such documents describe or address the location of the supported palladium in the catalyst, particularly, the relationship between such a location and the reaction selectivity.
In addition, the catalytic hydrogenation of an aromatic nitrile compound using a palladium/ruthenium-containing catalyst is reported in many documents. For example, U.S. Pat. No. 4,070,399 discloses a hydrogenation of phthalonitrile using a palladium/ruthenium catalyst. However, in the proposed hydrogenation, the aromatic ring is also hydrogenated together with the cyano group to give bisaminomethylcyclohexane, thereby failing to teach the production method of an aromatic ring-containing amino compound.
It is also reported that a catalyst containing ruthenium and a group VIII element such as palladium which are supported on a carrier having macro pores with specific diameter size is usable for the hydrogenation of aromatic dinitriles (JP 10-72377A and JP 10-101584A). However, these documents provide nothing about the kinds of the hydrogenated products, the supporting region of the metal components, the effect achieved by the binary system of metal components, and the working examples.